A person who has expressed a liking for you, and who you could (If you are a Virgin) shag if you wanted to, but you feel that:
a) You could do better than that person
b) Don't particularly trust them to take your virginity
c) They're a slut/whore/slag

Dave: "Hey, Mike, How'd things go with you and Katie go last night? I saw you walking upstairs with her..."
Mike: "Haha, not much, dude. We talked for ages but I think she's gonna be my "Get out of virginity free card" for a while"